Dec. 31 -- TUESDAY, Dec. 30 (HealthDay News) -- In another blow to the supposed cancer-fighting powers of vitamins C and E, new research suggests that supplement forms of the vitamins don't prevent the disease in women.
And another widely touted supplement, beta carotene, didn't help either, the new study found.
"Simply taking antioxidant supplements is insufficient to prevent cancer development," said study lead author Jennifer Lin, an assistant professor of medicine at Harvard Medical School.
But it's still a good idea to eat plenty of fruits and vegetables that are rich in nutrients such as antioxidants, Lin said.
Vitamin supplements have taken hits in a number of studies in recent years, with some research suggesting that supplements such as vitamins B, C, D, E, folic acid and calcium don't prevent cancer when taken in combinations or alone. The findings contradict other studies that had suggested the vitamins may have a protective effect due to antioxidants, which reduce damage to cells in the body.
For the new study, the researchers looked at a group of 8,171 women who were randomly assigned to take a supplement, a combination of supplements or a placebo. The supplements were vitamin C (500 milligrams a day), vitamin E (600 International Units every other day) and beta carotene (50 milligrams every other day).
The women, all over the age of 40, took part in the study from 1995 and 1996 until 2005, for an average of nine years. They all had cardiovascular disease or were at risk for it.
A total of 624 of the women developed cancer, and 176 died from it during the period of the study. The researchers didn't find any "statistically significant" evidence that the supplements either helped or hurt a woman's risk of developing cancer.
The findings were published online Dec. 30 in the Journal of the National Cancer Institute.
Why didn't the supplements prevent cancer, as some earlier research had suggested? One theory, Lin said, is that they might be effective in people who are poorly nourished, but not in well-nourished people such as the women in the study. She said some research has shown that diets lacking in antioxidants -- found in fruits and vegetables -- can lead to higher cancer rates.
The study isn't the final word, Lin said. "More studies need to be done to see who may benefit from antioxidant supplements. One trial study has suggested that men, compared with women, were more likely to gain benefits from supplementation with antioxidants in reducing cancer risk. However, such findings need verification."
Dr. Demetrius Albanes, senior investigator with the U.S. National Cancer Institute, who wrote a commentary accompanying the study, acknowledged that while the study results were disappointing, it's possible that the supplements could have had positive effects in women who weren't at high risk for cardiovascular disease, as were those in the study.
He added that the study indicated that vitamin E may have some benefit at preventing colon cancer specifically, as other research has suggested.
In the big picture, Albanes said, research shows that lower-calorie diets with plenty of fruits and vegetables do have benefits. "But right now, the issue of vitamin supplementation is still very much up in the air for men and for women," he added.
Learn more about the links between diet, exercise and cancer risk from the American Cancer Society.
SOURCES: Jennifer Lin, Ph.D., assistant professor of medicine, Brigham and Women's Hospital and Harvard Medical School, Boston; Demetrius Albanes, M.D., senior investigator, U.S. National Cancer Institute, Bethesda, Md.; Dec. 30, 2008, Journal of the National Cancer Institute, online